Nonalcoholic fatty liver disease (NAFLD) refers to a wide spectrum of liver disease ranging from simple fatty liver (steatosis), to nonalcoholic steatohepatitis (NASH), to cirrhosis (irreversible, advanced scarring of the liver). All of the stages of NAFLD have in common the accumulation of fat (fatty infiltration) in the liver cells (hepatocytes). In NASH, the fat accumulation is associated with varying degrees of inflammation, fibrosis and scarring of the liver.
NASH and NAFLD are frequently reported in both men and women, although it most often appears in women and is especially prevalent in the obese. Although the disease has been observed to be accompanied by several other pathological conditions, including diabetes mellitus, hyperlipidemia, hyperglycemia, all part of the “metabolic syndrome,” the cause and progression of the disease, as well as the causal or temporal relation to these conditions, is not well understood.
However, in patients suffering from NAFLD and NASH in particular, certain characteristics of liver tissue and abnormalities of function are typical. Specifically, fatty deposits, tissue degeneration, inflammation, cell degeneration, fibrosis, cirrhosis, elevation of free fatty acids and other such abnormalities have come to be associated with nonalcoholic steatohepatitis and are frequently seen in patients suffering from different forms of NAFLD.
The physiological condition that most commonly accompanies NASH is obesity, with approximately 70% and above of NASH sufferers also displaying clinically diagnosed obesity. NASH is particularly prevalent in obese patients who have undergone jejunal bypass to treat the obesity. In NASH patients, the extent of obesity tends to be generally correlated with the amount of steatosis and to be unrelated to non-insulin-dependent diabetes mellitus. However, non-insulin-dependent diabetes mellitus increases the prevalence of steatohepatitis especially in patients requiring insulin. Unless a massive amount of the excess body weight is eliminated, weight loss in patients before death does not appear to alleviate the steatosis and, somewhat paradoxically, obese patients who lost weight before death can have a higher incidence of steatohepatitis.
Even in NASH patients who do not consume any alcohol at all, liver biopsy specimens tend to mimic those seen in patients suffering from alcoholic hepatitis. However, a comparison of the two conditions reveals a higher incidence of vacuolation (indicative of diabetes) and steatosis in NASH as compared to alcoholic hepatitis. Patients suffering from alcoholic hepatitis also have a higher incidence of periportal and pericellular fibrosis and proliferation of the bile ducts. Overall, the symptoms and histological damage observed in alcoholic hepatitis patients are more severe than in NASH.
Currently, there is no established therapy for patients suffering from NASH. Weight loss is a common prescription, simply because obesity is frequently detected in patients suffering from NASH. The effect of a reduction in weight loss on NASH cannot be determined with certainty, however, because obese patients seldom maintain significant weight reduction. Thus, there is a need to find a treatment for NAFLD and particularly NASH.